As suggested by its name (sometimes also referred to as “no dig”), trenchless methods obviate the need to dig a substantially continuous trench or channel along the entire path to be taken by the underground tube or cable. Use of these methods reduces the extent of surface, underground and environmental disruption.
Trenchless methods involve the initial excavation of one or more ditches or pits, into which is lowered machinery and equipment, which forms a horizontal direction bore through a sidewall or bank of the pit at the required depth. Alternatively, the piping or such article to be installed is directly and forcibly pushed in the horizontal direction into the ground through a pit wall. Examples of trenchless methods that are hydraulic pipe ramming, moling using percussive heads, guided drilling techniques, and the like.
In the field of telecommunications, ever-greater deployment of optical fiber in the networks has now penetrated to the access network or local loop, i.e., the “last mile” in the path between the local exchange and customer premises. Optical fiber can be provided to various points along the path from the local exchange into customer premises, e.g., to the cabinet, the curb, and the premises or home (FTTH).
Typically, the market for FTTH connections is commercial or industrial in nature, which customers are relatively few in number and who are paying commercial rates for the installation of their optical lines. The provision of a similar connection to the vastly greater numbers of private, non-commercial premises throughout the country is an undertaking on a huge scale involving the installation of vast amounts of optical fiber at the local access level which had previously been served by copper.
In one FTTH implementation, blown fiber is deployed. This method is described in, e.g., EP 108590, where two points are optically connected in a two-stage process. First, a blown fiber tube is initially provisioned along the path between the two points. Subsequently, as and when the optical connection is required, a fiber or fiber unit (comprising a number of individual fibers) is installed through the waiting fiber tube, by “blowing” it through the tube, whereby the fiber or fiber unit is pulled along through the tube by the effects of viscous drag.
Various types of tubing or ducting for blown fiber use exist. Mini- or micro-ducts are one type of blown fiber duct which is used particularly nearer the customer end in the access network. For a FTTH application, a number of micro-ducts are initially bundled into a larger duct at the exchange end, and gradually broken out along the path in a branching formation in the direction of the customer. These micro-ducts are hollow tubes typically made from plastics and range in size from 6 to 22 mm in OD diameter.
Currently, blown fiber tubes are installed within pre-installed duct or by direct burial either by surface-digging trenches which extend the length of the installation, which is then reinstated after the tubing has been laid. It is possible to cut a slot into the ground which is substantially narrower than a standard trench, which reduces surface disruption, but this method requires specialized cutting equipment. Trenchless methods are also deployed, using commercial pipe ramming, moling and such-like commercial equipment. As can be expected, both surface and trenchless methods currently in use can generate considerable disturbance either on the ground surface level and/or in the amount of noise, fumes, congestion and the like the installation process creates.
One response to the need for less disruptive duct installation methods is to use manually-driven pushers or borers which do not employ heavy equipment or noisy percussive hammers or rammers with all the associated pollution and disruption. Such pushers are described in U.S. Pat. No. 1,188,336, U.S. Pat. No. 1,208,472, U.S. Pat. No. 2,519,680 and U.S. Pat. No. 3,645,502, wherein the apparatus is set on the floor of a trench or pit. The operative stands within the trench and operates a handle or lever arm to move (by pushing or pulling) a pipe or ducting through a pit sidewall and/or through the ground and in a horizontal or sideways direction into the ground. A pipe-engaging section located at the lower end of a lever arm engages with the pipe as the lever arm is operated by swinging it about a pivot or fulcrum so that its lower end describes an arc. This repeated action drives the pipe into the pit wall and thus into the ground. In use, the pipe-engaging section grips the pipe and pushes it forward on a pull stroke of the handle, and then releases it on the push stroke to allow the re-engagement with another section of the pipe. These pushers include the use of guides (e.g., plates) to ensure that the trajectory taken by the pipe does not veer too far off course while it is pushed through the ground, which is a result of the tendency of the pipe-engaging sections to send the pipe along a curved trajectory resulting from the curved path described with the swinging of the lever arm. Withdrawal of installed pipes is also provided for, by the reconfiguration of parts making up the pipe-engagement section, or else providing that the frame is capable of being taken apart so that the pushing apparatus may be taken out of the pit and positioned to face the opposite way.
Such pushing apparatus are not optimized for use in the installation of FTTH optical fiber ducting on the scale described above for various reasons. For example, the pits occupied by the prior art apparatus are relatively large, as having to accommodate the apparatus as well as the operative within it. With potentially so many pits to be dug at the customer end, any reduction in disruption would be desirable. This is so especially as residential customers may be less tolerant than, e.g., commercial customers of having their established gardens, driveways and private property torn up with an excessively large pit. It would also be advantageous to reduce the number of parts in the apparatus, to minimize exposure to the dirt and debris that may be expected in a pit.
Further, the pipe-engaging portions described in the prior art impart a high degree of crushing force when gripping the tube to push it forward. While metal pipes or solid boring rods may be able to withstand such forces, hollow mild steel push tubes and micro-duct tubes (usually made from plastics), may be more fragile and need greater care in handling. It would also be desirable to quickly and easily reconfigure the pushing apparatus to change its pushing direction for the withdrawal of pipes from the ground, without need for the operative to turn the entire device around completely, or to rearrange relatively small components with possibly gloved frozen fingers while standing in a dark cold wet ditch.
It would therefore be desirable to provide apparatus and methods addressing the above issues for the trenchless installation of micro-ducts and such other piping or tubing especially to accommodate FTTH telecommunications cables and fibers.